It's defined as a C macro in hv.h. From that file:

/* hash a key */
/* FYI: This is the "One-at-a-Time" algorithm by Bob Jenkins
 * from requirements by Colin Plumb.
 * (http://burtleburtle.net/bob/hash/doobs.html) */
/* The use of a temporary pointer and the casting games
 * is needed to serve the dual purposes of
 * (a) the hashed data being interpreted as "unsigned char" (new since
+ 5.8,
 *     a "char" can be either signed or signed, depending on the compi
+ler)
 * (b) catering for old code that uses a "char"
 */
#define PERL_HASH(hash,str,len) \
     STMT_START { \
        register const char *s_PeRlHaSh_tmp = str; \
        register const unsigned char *s_PeRlHaSh = (const unsigned cha
+r *)s_PeRlHaSh_tmp; \
        register I32 i_PeRlHaSh = len; \
        register U32 hash_PeRlHaSh = 0; \
        while (i_PeRlHaSh--) { \
            hash_PeRlHaSh += *s_PeRlHaSh++; \
            hash_PeRlHaSh += (hash_PeRlHaSh << 10); \
            hash_PeRlHaSh ^= (hash_PeRlHaSh >> 6); \
        } \
        hash_PeRlHaSh += (hash_PeRlHaSh << 3); \
        hash_PeRlHaSh ^= (hash_PeRlHaSh >> 11); \
        (hash) = (hash_PeRlHaSh + (hash_PeRlHaSh << 15)); \
    } STMT_END
[download]

After Compline,
Zaxo

Ah, the "One-at-a-Time" algorithm. That's quite simple in comparison to the first one on the cited page, his "new hash". That takes 12 bytes at a time with a 12-byte internal state, but it is actually faster (order of 6n instead of 9n) because it handles more in a gulp.

I was thinking that Perl used the "newhash" now.

—John

Is this the hash you are thinking of? If so, I have an implementation in perl which seems reasonably quick but I haven't managed to verify it as a correct implementation yet. Of course, an inline C or XS version would be much quicker if you have that option open to you.

..and remember there are a lot of things monks are supposed to be but lazy is not one of them

The listing at the beginning of that page -- yes, that's what I'm looking for. I'd be happy to start with your code, since I'd need to verify anything I wrote anyway (and I'll let you know the results).

—John